1. Filed of the Invention
The present invention relates generally to an optical fiber connector to be employed at junctions of optical communication fibers. In particular, the invention relates to an optical fiber connector which can easily secure dimensional accuracy required for ultra high-speed communication.
2. Description of the Related Art
Optical fiber connectors to be employed for connecting optical communication fiber cables are required to have reduced insertion loss and reduced return light loss, in order to secure transmissibility. Accordingly, ferrules which retain end portions of optical fibers, having, for example, a flat or convex spherical abutment face at the distal end are employed depending on the transmission performance.
An optical fiber connector employed for connecting ultra high-speed communication optical fibers (such as for image transmission) has a slant convex spherical face as shown in FIG. 3, which illustrates connector ends each having a slant convex spherical face, which are abutted against each other. The slant convex spherical faces 101 can bring end faces of two opposing optical fibers 102 into direct contact with each other at a point 103 on the optical axes f of the optical fibers 102. Further insertion loss and return light loss can be reduced by tilting the abutment plane 104 in contact with the convex spherical faces 101 at this abutment point 103. The reference number 106 shows a ferrule for retaining the optical fiber 102 at the end of the optical fiber connector.
Meanwhile, the optical fiber connector has a conical tapered portion 107 around the periphery of the slant convex spherical face 101 at the end of the columnar ferrule 106 as shown in FIG. 4, in which the connector shown in FIG. 3 is tapered at the and. This slant convex spherical face 101 is employed as a fiber connection guide and is formed such that the apex 108 of the spherical face may be located at a position offset from the axis f of the ferrule corresponding to the optical axis when the slant convex spherical face 101 is subjected to spherical polishing employing an ordinary elastic polishing plate.
The reason is as follows. According to the conventional spherical polishing treatment employing an elastic polishing plate, a material to be polished is subjected to polishing at the end face of a protruded portion as a reference shape. Thus, a high-accuracy polished spherical face having an apex at the center of the upper end face can easily be formed with an angle of inclination of the abutment plane 104 being secured at the apex of the spherical face.
Meanwhile, referring to the central point at the end face of the protruded portion having a polished reference shape, since the abutment plane 104 is angled, the central point 108 of the protruded portion 104a, which is formed by the abutment plane 104 and the conical face 107a of the tapered portion 107, is offset from the ferrule axis f corresponding to the optical axis.
A polished spherical face is formed with the central point 108 as the apex. Therefore, the apex 108 of the slant convex spherical face 101 (formed based on the abutment plane 104) contains an error corresponding to the deviation E from the point 109 on the ferrule axis f.
This deviation of the apex induces reduction in transmissibility, so that these optical fiber connectors cannot be employed for connecting optical fibers for ultra high-speed communication. In addition, the deviation increases as the depth of polishing achieved by the elastic polishing plate is increased, and it cannot be eliminated even by adjustment of the polishing treatment.
In order to obviate this deviation of the apex, there is proposed a method of polishing the ferrule by rotating the elastic polishing plate with the point 109 on the ferrule axis f as the center of rotation, or a method as shown in FIG. 5, in which a columnar portion 110 having a reduced diameter is formed at the end of the tapered portion 107, and a slant convex spherical face 101 is formed at the end of this reduced-diameter columnar portion 110.
However, in the former polishing method, where the elastic polishing plate is rotated about the point 109 on the ferrule axis f so as to coincide with the apex of the spherical face, a special polishing device requiring accuracy of the rotational shaft and microscopic high-accuracy positioning is required. In the latter polishing method, where a reduced diameter columnar portion is provided between the tapered portion and the slant convex spherical face, the steps of processing the ferrule are complicated, and the rigidity at the end of the ferrule is reduced since the reference abutment point is present at the end of the reduced-diameter columnar portion protruding from the tapered portion. This may lead to problems in durability, including unstable transmission.